Complaint Review: Flagship merchant

Flagship merchant services just closed my account and told me that they would hold my funds for 180 days. When we first opened merchant account with them, the monthly limit was set to $2500. after several months, our sales were successful and increased high volume of sales and that's the reason of closing my account without advance notice. I could found out the merchant account was closed because customers emailed that they can't process order by their credit card.
They closed my account because our sales volume is much higher than the monthly limit and most of them are international transaction. they told that they would hold the whole fund of more than $40000 just in case of charge back. However, I found that they withdrew $3200 from my checking account without advance notice or reasons. Is the $40000 not enough for cover any charge back may occur?
In addition, I didn't have any charge back so far.
I don't know where and whom I should contact for this matter. Do I need to contact lawyer for this incident?